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Aviation History
2003
2003 - 1176.PDF
Systems mechanical circuit-breakers, providing load management benefits and improved diag nostic health monitoring and system upgrade potential. Airbus has demanded an equally radical rethink on hydraulics. The A380 has a par tially decentralised 350bar (5,000lb/in2) hydraulic system, with many of the flight controls powered by electro-hydraulic actua tors using a local hydraulic reservoir - the first of its kind on a commercial transport. The system, including eight engine-driven pumps (EDPs), hydraulic lines and hoses, is being supplied by Eaton, while Messier- Bugatti is supplying the hydraulic fluid collectors and filters, and the electro- hydraulic actuators for the fight controls. All previous Airbus aircraft have used a more conventional 210bar hydraulic working pressure, and the 66% pressure increase on the A380 was driven primarily by weight requirements. John Halat, director of R&D at Eaton Aerospace, says narrower tubing and less oil volume are the chief advantages. "Total weight savings realised in the system are about 2,200lb [1,000kg]," he says. There is an estimated 1,000m of hydraulic piping and tubing in the A380, about one-third of which is pressurised to 350bar. Halat says the first production configura tion EDPs are scheduled to be delivered to Airbus this month, having already completed 1,000 hours of testing with Airbus and R-R. The production EDPs will have a clutch - new to Eaton's commercial products. Halat says Airbus asked for clutches so that EDPs could be isolated in flight if required, and to allow flight dispatch with an inoperative pump. "Other new features include impellers for improved low-pressure operation and wmmmmmsmm attenuators which can guarantee less than 1 % pressure error," he adds. The relatively narrow hydraulic lines bene fit from Eaton's Rynglok titanium tube fittings, 1,100 of which are used on the A380, and 150 more are used for tube assemblies on the MLGs. The fittings were designed specifically for the 350bar hydraulic systems on the Boeing F-18E/F Super Hornet and the Bell Boeing V-22 Osprey programmes, and can be installed in-situ in the aircraft, says Eaton. To with stand the higher pressures, Eaton's Aeroquip hosing, which is used on the land ing gears, also has titanium fittings and Kevlar reinforcement, while traditional stain less steel-reinforced hosing is used on the lower pressure return lines. Brian Mack, Aeroquip product manager at Eaton, says the qualification of the Kevlar reinforced hosing, which includes 300,000 impulse cycles at 150% of operating pres sure, should be complete by June, and Halat says first hardware for the MLG's hydraulics will be handed over to Goodrich in September. Reliability requirements A major challenge for Eaton was Airbus's increased reliability requirements for the sys tem. Phil Galloway, engineering manager at Eaton's Vickers Fluid Power, says: "Traditionally, we aim for 25,000 hours' mean time between failure, which sizes our bearing and rotating components. For the A380, Airbus requested 50,000 hours. We compro mised at 40,000, but it's still a real challenge." In its partially decentralised hydraulic sys tem, the A380 will have only two main hydraulic circuits instead of the three previ- Conventional servocontrol Accumulator Servo-valve Electro-hydrostatic actuator (EHA) Electronics Mode selector device T !1 Servocontrol replaced by an electric motor pump Pump Hydraulic block h Hydraulic system (power) ^ Motor Servocontrol in normal operation EHA in back-up FLIGHT Hamilton ously used on Airbus aircraft. The third Sundstrand's emergency circuit will consist of indepen- first full AGS dent decentralised hydraulic generating testis systems located close to the actuators, scheduled allowing the third circuit to be replaced by an forAugust electrical circuit, saving a considerable this year, amount of weight. ahead of The primary and secondary FCSs use delivery to electrically powered instead of hydraulically Airbus by powered systems, resulting in the near dis- year-end appearance of hydraulic circuits in the A380's wings and fin. The "more electric air craft" developments have led to the adoption of electro-hydrostatic actuators (EHAs) and electric backup hydraulic actuators (EBHA) in the FCS. The EHAs convert electrical power into hydraulic power locally through an electric motor and a pump which then moves the piston jack. The hydraulic circuit is con strained within the actuator and is totally independent of the aircraft hydraulic supply, saving weight and hydraulic complexity. The EBHAs, on the other hand, are more con ventional in that they remain connected to the main hydraulic supply and use the sup ply in normal operation, transitioning to electrical power supply in backup operation. Although not cost- and weight-effective, the EBHAs improve safety by having a backup to potential hydraulic failure. A further saving in hydraulic demand comes from the use of an electrical thrust reverser actuation system (ETRAS). Developed by Honeywell and Hispano- Suiza, the ETRAS also offers a reduced risk of inadvertent deployment, says Honeywell, as well as improved maintainability com pared with traditional hydraulic or pneumatic solutions. Thrust reversers are fitted only to the inboard engines on the A380, again to save weight. The software for the FCS, along with all the other system software on the aircraft, sits on the 32-unit Thales Avionics-supplied inte grated modular avionics (IMA) suite, developed with Diehl Avionik Systeme of Germany. The IMA suite comprises standardised electronic boards and modules and uses a common Arinc 653 operating system. The XIV 20 26 MAY 2003 FLIGHT INTERNATIONAL SUPPLEMENT
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